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82                           METALLURGY OF IRON AND STEEL.
vary through wide limits, contents as high as three per cent, being sometimes used in admixture. Such a large amount gives a brittle iron, but it gives increased fluidity, which is advantageous in making complicated castings. For ordinary castings a content of about one-half of one per cent, is usual. For the making of steel by the acid Bessemer process, as used throughout America, the iron must not contain over one-tenth of one per cent, of phosphorus. Inasmuch as nearly two tons of ore are used for a ton of pig-iron, and as the coke and limestone both contribute phosphorus, it will be seen that suitable "Bessemer ore" should have less than, one-twentieth of one per cent, of this element. The steel ma'ker classifies all the ores of the world by the second and third place decimal of one per cent, of phosphorus.
Sulphur: Iron ores as a rule are low in sulphur, but coke always contains a considerable amount, one-half of one per cent, being very low and one and one-half per cent, quite common. If the blast furnace is working well with a good slag and a, high temperature, almost all of this sulphur will unite with the. lime and be carried off in the cinder and the iron will contain less than one-twentieth of one per cent, of sulphur; but if the furnace is cold and the slag not sufficiently basic, the metal may contain over half of one per cent. Sulphur tends to hold carbon in combination, and therefore iron containing a high percentage is usually hard and brittle, this being especially the case when the percentage of silicon is low, a condition often existing, as a cold furnace is likely to produce high sulphur and low silicon.
Manganese: Iron ores generally contain more or less manganese, but usually in small proportion. Moreover, it is not all reduced in the furnace, some of it passing away in the slag. The ordinary pig-iron of commerce carries less than one per cent., but two per cent, is not uncommon. In the manufacture of steel a large amount of spiegel iron is used, by which is meant an iron containing from 10 to .26 per cent, of manganese. Ferro-manganese is also used containing up to 80 per cent. Manganese causes, the carbon to remain in combination so that spiegel iron is hard and brittle. The totujj^eontent of carbon is higher in manganiferous irons, being often up to 7 per cent, in 80 per cent, ferro-manganese.
Other Elements: Many other elements are often found. Copper is easily reduced in the furnace, and some irons contain over one